"This project evaluates a method for the removal of trihalomethane (THM) precursors from surface water sources. The site of the project. Cross Lake in Shreveport, Louisiana, represents sources in the southern United States with high concentrations of THM precursors. In one phase of the project, a pilot plant was operated for 80 weeks to test the combination of ozone and granular activated carbon (GAC) for THM precursor removal. An important objective of the pilot study was to investigate the possibility of microbiological degradation of precursors In the GAC columns and the effect of preozonation on this process. The combination of ozone and GAC is sometimes referred to as biological activated carbon (BAG). Analysis of the pilot plant data shows microbiological activity to be a significant contributor to the removal process for total organic carbon (TOO and trihalomethane formation potential (THMFP) in GAC columns under the conditions tested. In the initial stages, the removal mechanism appears to be primarily adsorption. But, after 50 x 103 bed volumes of water have been processed, only microbiological removal remains. During the Interim period, both adsorption and microbial processes appear to contribute to TOC and THMFP removal. Comparison of costs associated with the addition of GAC and BAG to traditional water treatment plants of 100-, 10-, and 1 -mgd capacities shows that, for the conditions of this study, the addition of ozone was not cost effective in extending the time between reactivations of the GAC. In a second phase of the project, studies were conducted at Shreveport's Amiss treatment plant complex to define the extent of their THM problem. Results there showed high concentrations of THM's. Alternatives for lowering the concentrations to less than 0.10 mg/L Include addition of GAC and conversion to chloramination. In either case, some type of oxidant will be required for manganese control."--P. .